You should change all the passwords as BobTheFisherman suggests.
If you either:
a) allowed unknown software to be installed, or
b) gave away your Admin password
... then your computer is compromised in ways that are hard to know. To secure your Mac again:
• If you do have a backup from before you granted access, you should ERASE your drive and do a full restore from before you granted access to those lying criminals.
• If you do not have a previous Backup, you should make one now, ERASE your drive, Install Mac OS from a fresh or saved download, and then re-install ONLY your files -- get your third-party Applications from their original sources, or restore them one at a time so that you Install exactly what you expect and nothing more.
If you need help in finding easy ways to make a Backup, just ask.
This sounds draconian, but is about the only way to assure that you do not still have "hitchhikers" that those creeps installed.